<button class="btn">
    <span class="btn__visible">Buy Now</span>
    <span class="btn__invisible">Only 2 Left</span>
</button>
<style>
/* From Uiverse.io by joe-watson-sbf - Tags: gradient, button, hover, shop */
.btn {
  font-size: 14px;
  font-weight: 300;
  text-transform: uppercase;
  line-height: 8px;
  border-radius: 30px;
  border: none;
  background-image: linear-gradient(120deg, #f093fb 0%, #f5576c 100%);
  color: #fff;
  position: relative;
  overflow: hidden;
  cursor: pointer;
}

.btn > * {
  display: inline-block;
  transition: all ease-in-out .5s;
}

.btn__visible {
  padding: 1.2rem 3rem;
  text-align: center;
}

.btn__invisible {
  width: 100%;
  position: absolute;
  padding: 1.2rem 0;
  left: 0;
  top: -100%;
}

.btn:hover {
  background-image: linear-gradient(160deg, #f093fb 0%, #f5576c 100%);
}

.btn:hover .btn__visible {
  transform: translateY(100%);
}

.btn:hover .btn__invisible {
  top: 0;
}

.btn:focus {
  outline: none;
}

</style>
